[BUG] Bad parallel performance when optimizing a group

Describe the bug

In Windows, when optimizing a shader group in parallel, the performance is almost as the optimization is performed sequentially.

I tracked down the problem, in src\liboslexec\llvm_instance.cpp.

In the block inside if (use_rs_bitcode()) {
the call to ll.validate_global_mappings(names_of_unmapped_globals); triggers a global lock inside llvm.

commenting out the validation solves the problem. A possible solution would be to have an option to turn off validation, so I can turn it on only during debugging.

OSL version and dependencies

• OSL branch/version: 1.14.5.1
• OS: Windows
• C++ compiler: MSVC 2022
• LLVM version: 19.1.7
• OIIO version: 3.0.2

src/liboslexec/llvm_instance.cpp の use_rs_bitcode() ブロックから開始し、ll.validate_global_mappings(names_of_unmapped_globals) の呼び出しを調査します。Windows で shader グループが並列に最適化される仕組みを追跡し、その後、通常の最適化では検証を無効化し、デバッグ時には有効なままにできることを、ほぼ逐次実行になるようなパフォーマンスへの影響なしに確認します。